Piezoelectric user interface

ABSTRACT

The invention relates to an apparatus ( 1 ) comprising a keypad ( 2 ), and means for generating a tactile response to a user of the apparatus when a key in said keypad is pressed. In order accomplish a simple construction requiring a minimum of space, said means for generating a tactile response include at least one piezoelectric element ( 3 ) arranged to generate vibration which is forwarded to the user via a key when said key is pressed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a solution for generating tactile feedback toa user of an apparatus when the user presses a key on a keypad of theapparatus. Such tactile feedback, which is perceptible by touch, makesit possible for the user to know when the key has been pressed long andhard enough for the apparatus to register the keystroke.

2. Description of the Prior Art

Several different solutions are previously there known for indicating toa user of an apparatus that a key has been pressed long and hard enoughto enable the keystroke to be registered.

A previously known solution is to provide each key with a mechanismwhich produces a “click” that can be felt and/or heard by a user whenthe user presses a key. The problem with such prior art mechanicalsolutions is the space required by the mechanism. It is in practicenecessary to design the key such that the key is allowed to move apredetermined distance before it reaches the location where the “click”is generated. The space required by the movement and the space requiredby the mechanism itself mean that the entire keypad turns out to berelatively thick.

Another previously known solution is to provide an apparatus with meansfor generating a sound signal each time a keystroke is registered. Sucha solution has typically been used in connection with thin membranekeypads since this solution does not increase the thickness of thekeypad because the means necessary for generating the sound can belocated somewhere else in the apparatus. The problem with this prior artsolution is, however, that the “beep” generated in connection with eachkeystroke is rather annoying, and most users would thus prefer to turnoff such a “beep”. This, however, is not possible in practice becausethen the user will not know when a keystroke has been registered, sincethis solution does not give any tactile feedback to the user. Thus theuser might, by mistake, press the same key several times although theintention was only to press once.

SUMMARY OF THE INVENTION

An object of the present invention is to solve the above-mentionedproblems and to provide an apparatus with improved means for generatingtactile feedback to a user in connection with a keystroke.

Another object of the present invention is to provide an apparatus withmeans for generating tactile feedback which requires less space than inthe previous solutions.

The above-mentioned and other objects of the invention are achieved byan apparatus that includes a keypad and means for generating a tactileresponse to a user of the apparatus when a keypad is pressed. The meansfor generating a tactile response include at least one piezoelectricelement arranged to generate vibration which is forwarded to the uservia a key when said key is pressed.

The invention is based on the idea of utilizing a piezoelectric elementin an apparatus in order to provide the user with tactile feedback inconnection with a keystroke. The piezoelectric element is small enoughto be integrated such an element into a membrane keypad of an apparatus,for instance. A piezoelectric element can be controlled to createvibration which propagates to the key pressed by a user. The spaceneeded in the prior art solutions for a mechanism to produce a suitable“click” at each keystroke can be significantly minimized by theinvention, since the piezoelectric element can create vibration wherethe key which has been pressed is pushed back in a direction towards afinger of the user.

The most significant advantages of the present invention are thattactile feedback can be generated employing a simpler solution whichrequires less space than the prior art solutions, the energy consumptionin connection with generating tactile feedback is low, and that theprice of the means necessary for generating tactile feedback isrelatively low.

In a first preferred embodiment the present invention, the apparatusincludes a controller arranged to identify a key in said keypad pressedby the user, and to check whether or not the pressed key has beenavailable as an option at that particular moment. If the key has beenavailable as an option, a piezoelectric element is controlled togenerate first kind of vibration. If, on the other hand, the key has notbeen available as an option, a piezoelectric element is controlled togenerate second kind of vibration. This embodiment makes it possible togive the user such tactile feedback that the user can immediately feelwhether the user has pressed a “right” key or a “wrong” key.

In a second preferred embodiment, the apparatus is a media terminalcomprising means for establishing telecommunication connections, and theapparatus is arranged to generate an alerting sound signal with said atleast one piezoelectric element in response to an incoming call. Thisembodiment is advantageous as it makes it possible to save space in themedia terminal, since the alerting sound signal can be created with thesame piezoelectric element as is used to generate tactile feedback whena key is pressed. This can be achieved when the media terminal isprogrammed to feed such a signal to the piezoelectric element that thepiezoelectric element generates vibration that can be heard.

In a third preferred embodiment, the apparatus is a media terminalcomprising means for establishing telecommunication connections, andsaid apparatus is arranged to generate an alerting vibration signal withsaid at least one piezoelectric element in response to an incoming call.This embodiment makes it possible to save space by eliminating an extracomponent used in the prior art media terminals in order to accomplishvibration alerting. Instead, it is possible to generate such vibrationalert by using the same piezoelectric element as is used to generatetactile feedback when a key is pressed. In this embodiment, it might beadvantageous to have several piezoelectric elements in the mediaterminal since this makes it possible to generate very strong vibration.The user thus feels the vibration even if the media terminal is locatedin a pocket.

Preferred embodiments of the apparatus according to the presentinvention are disclosed in the attached dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in closerdetail by way of example and with reference to the attached drawings, inwhich

FIG. 1 a shows a first preferred embodiment of an apparatus according tothe invention,

FIG. 1 b shows an exploded view of parts associated with the keypad ofthe apparatus in FIG. 1 a,

FIG. 1 c shows a sectional view of the parts in FIG. 1 b,

FIG. 2 shows a second preferred embodiment of an apparatus according tothe invention,

FIG. 3 a shows a sectional view of a third preferred embodiment of anapparatus according to the invention,

FIG. 3 b shows a side view of some of the parts in FIG. 3 a,

FIG. 3 c shows a top view of the parts in FIG. 3 b,

FIGS. 4 a to 4 f show different electrical waveforms fed to anpiezoelectric element.

FIG. 5 shows an electric circuit with a piezoelectric element,

FIGS. 6 a and 6 b show how a waveform can be varied, and

FIG. 7 shows another electric circuit with a piezoelectric element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 a to 1 c illustrate a first preferred embodiment of theinvention. The apparatus 1 in the example of FIGS. 1 a to 1 c is a mediaterminal comprising means for establishing telecommunicationconnections. These means include a radio transmitter and a radioreceiver for establishing, for instance, phone calls via a cellularmobile communication system. The mobile communication system may be, forinstance, a GSM system (Global System for Mobile communications) or athird generation mobile communication system.

FIG. 1 a shows an apparatus comprising a keypad 2 and a display. FIG. 1b shows an exploded view of parts associated with the keypad 2 of theapparatus 1 in FIG. 1 a, and FIG. 1 c shows a sectional view of theparts in FIG. 1 b. The keypad 2 is a flexible membrane keypad which mayconsist of one layer (as shown in the FIGS. 1 b and 1 c) or of severalcooperating layers. The locations of the keys are visible on an upperside of the keypad 2. When a user presses one of the keys on the keypad2, an impulse corresponding to the pressed key is generated andforwarded to a controller 8 (which is schematically shown in FIG. 1 b).

The apparatus also includes a piezoelectric element 3 arranged contact alower side of the keypad 2. The piezoelectric element 3 is, in theexample of FIG. 1 b, connected to controller 8 such that the controllermay control the function of the piezoelectric element. It is naturallyalso possible to have separate controllers for the keypad and thepiezoelectric element.

The piezoelectric element 3 includes a metallic plate 6 to which a piezotransducer 7 has been attached. Many materials, such as quartz, lithiumniobate and lead-zirconate-lead-titane (PTZ) exhibit some form ofpiezoelectric effect and can thus be used in a piezoelectric element.

There are several piezoelectric elements commercially available whichcan be used in an apparatus according to the present invention. Analternative is to use a piezoelectric element GPB-A-25 0.9E availablefrom Union Enterprise Co., 1326, Life Officetel, 61-3 Yoido-Dong,Yeoungpo-Ku, Seoul, Korea. In this case, the thickness of thepiezoelectric element 3 in FIGS. 1 b and 1 c may be 0.15 mm, and thewidth and length of the rectangular plate 6 may be 40 mm×50 mm.

The piezoelectric element 3 is supported by a soft foam frame 4 whoseback side is supported by a hard layer 5. The hard layer 5 might be apart of the body of the apparatus 1.

When the controller 8 detects that the user has pressed one of the keyson the keypad 2, the controller feeds an electrical impulse to thepiezoelectric element 3. This impulse causes the piezoelectric element 3to vibrate. As the keypad 2 is a flexible membrane keypad whose lowerside is in direct contact with the piezoelectric element, the user ofthe keypad 2 feels the vibration with his finger. The user thus receivestactile feedback informing the user that the key has been pressed hardand long enough in order for the apparatus to register the keystroke.

Suitable vibration can be generated when the voltage of the signal fedto the piezoelectric element is around 150 . . . 200 VDC and a piezotransducer whose diameter is 25 mm is used. The capacitance of thepiezoelectric element may in this case be around 60 nF in order toproduce vibration which can be felt by the user. If the apparatus is amedia terminal, the previously mentioned voltage is not usuallyavailable in the media terminal. A way to produce the required voltageis to include a piezoelectric transformer in the apparatus.

Two kinds of piezoelectric effect exist: direct effect and inverseeffect. With the direct effect, placing a force or vibration (stress) onthe piezoelectric element generates a charge. The inverse piezoelectriceffect means that applying a field at the same polarity of the elementresults in a dimensional increase, and fields of opposite polarityresult in a decrease.

A piezoelectric transformer (known from the prior art) uses both theinverse and the direct piezoelectric effect. The inverse effect is usedsuch that a sine-wave voltage is fed to a “first” piezoelectric element.This voltage causes this first piezoelectric element to vibrate. A“second” piezoelectric element is attached to the first element suchthat the vibration generated by the first piezoelectric element placesstress on the second piezoelectric element, thus enabling an outputvoltage to be obtained at the output of the second piezoelectricelement. Suitable dimensioning of the piezoelectric elements enables adesired output voltage to be obtained. Practical implementations existwhere a piezoelectric transformer with dimensions of: 20 mm×6 mm×1 mmcan be used to obtain an output voltage of 150 V (effect 1 W) when theinput voltage is 3V. Such a piezoelectric transformer can be used forinstance in a multimedia terminal in order to achieve the voltagerequired for the piezoelectric element of the present invention.

In an embodiment of the present invention the controller 8 can beprogrammed to generate different kinds of vibration depending on thesituation. A possibility is that the controller 8 is programmed tocheck, at each keystroke, whether the pressed key has been available asan option at that particular moment. If the key has been available as anoption, the controller can control the piezoelectric element 3 togenerate first kind of vibration, in other words tactile response, tothe user. If, however, the pressed key has not been available as anoption, the controller can control the piezoelectric element 3 togenerate second kind of vibration. The user, by sensing the second kindof vibration with his finger or by hearing the sound of the secondvibration with his ears, then knows that he has pressed the wrong key.If the apparatus I is a multimedia terminal that can be used fortelecommunication connections, the piezoelectric element 3 (or elements,if the multimedia terminal includes several piezoelectric elements) canbe used to generate an alerting vibration signal. The prior art elementsused in known mobile phones can thus be eliminated by a much smaller andlighter piezoelectric element. In this case, the controller 8 controlsthe piezoelectric element (or elements) to generate vibration of afrequency and intensity that can be felt by the user who has themultimedia terminal in his pocket. It is also possible to use thepiezoelectric element 3 to generate an alerting sound signal. No extrabuzzer is then needed in the multimedia terminal for this purpose.

The same piezoelectric element can easily be used for the abovementioneddifferent tasks in practice since the only necessary change is toprogram the controller to feed different kinds of waveforms to thepiezoelectric element 3. FIGS. 4 a to 4 f show examples of waveformswhich can be fed to a piezoelectric element.

FIG. 2 shows a second preferred embodiment of an apparatus according tothe invention. FIG. 2 only shows parts of the apparatus associated withthe keypad.

The keypad in the embodiment of FIG. 2 is very similar to the one shownin FIGS. 1 a to 1 c. The only differences are that the apparatusincludes four piezoelectric elements 3′ in the embodiment of FIG. 2, andthat the soft foam frame 4′ and the hard layer 5′ have a slightlydifferent shape in order to receive and support the four piezoelectricelements 3′.

Controller 8′ is programmed in a slightly different manner than thecorresponding controller in the embodiment of FIGS. 1 a to 1 c. Thecontroller is thus capable of controlling the four differentpiezoelectric elements 3′.

The keys on the keypad 2 of FIG. 2 are divided into four groups, forinstance. The controller 8′ includes a memory wherein information isstored about which key belongs to which group. This memory also containsinformation about which piezoelectric element is located closest to eachgroup of keys.

When a user presses a key on the keypad, the controller 8′ identifiesthe pressed key. When the key has been identified, the controller checksto which group of keys the pressed key belongs, and after that, thecontroller further checks which piezoelectric element is located closestto the identified group of keys. This closest piezoelectric element isthen controlled by the controller to generate tactile feedback to theuser as explained in connection with FIGS. 1 a to 1 c. In thisembodiment, the user of the apparatus feels vibration which only causesa region close to the pressed key to vibrate.

The other functions of the controller 8′ are similar to those explainedin connection with the embodiment of FIGS. 1 a to 1 c. A furtheradvantage achieved by using several piezoelectric elements is that thealerting vibration signal can be much stronger than when only onepiezoelectric element is used. It is also possible to modify thevibration alerting, for instance, by synchronizing the vibrations of thedifferent piezoelectric elements.

FIG. 3 a shows a sectional view of a third preferred embodiment of anapparatus according to the invention. FIG. 3 b shows a side view of someof the parts in FIG. 3 a, and FIG. 3 c shows a top view of the parts inFIG. 3 b.

Only the parts of the apparatus which are associated with the keypad areshown in FIGS. 3 a to 3 c. The apparatus of FIGS. 3 a to 3 c is providedwith a touch screen keypad, in other words a combination of a displayand a keypad, where the user presses keys shown on the screen.

A touch-sensitive transparent cover 2′ forms an upper surface of thetouch screen keypad. Each corner of the rectangular cover 2′ issupported by a piezoelectric element 3. The piezoelectric elements 3 aresimilar to those shown in FIGS. 1 a to 1 c and they are supported, forinstance, by a Printed Circuit Board (PCB) 10 of the apparatus. A softfoam frame has, however, been arranged between the PCB 10 and the metalplate 6 of the piezoelectric elements 3.

The PCB 10 also supports a display circuit 9. This display can be usedboth to display information to the user of the apparatus and to displaythe numbers or letters of the “keys”, which, in the embodiment of FIGS.3 a to 3 c, consist of areas on the touch-sensitive cover 2′. The touchsensitive-cover is, in the example of FIGS. 3 a to 3 c, attached to theapparatus by means of a frame 11, which, via an elastic strip 12, keepsthe support 2′ in place, allowing it to vibrate, however.

Tactile feedback given to a user in connection with a keystroke isgenerated by one or more of the piezoelectric elements 3 generatingvibration that causes the entire cover 2′ to vibrate.

The piezoelectric elements can be controlled as explained in connectionwith FIGS. 1 a to 1 c to give tactile feedback which enables the user todetermined whether or not the pressed key was available as an option,give a vibration alert in connection with an incoming call, and to givesound vibration in connection with an incoming call.

FIGS. 4 a to 4 f show examples of waveforms which can be fed to apiezoelectric element in connection with different tasks. FIG. 4 a showsa regular key click. FIG. 4 b shows a multiple click that can be used toindicate an error, for example. It can also indicate that a certain keyor function has been activated, or that the n:th key of an array of keyswas pushed by clicking n times as verification, making visualverification unnecessary. Another kind of indication is depicted in FIG.4 c. Here rapid sequential clicks making a sound 13 is heard after thekey click. This sound can comprise a complex group of pulses as will bedescribed.

A waveform as depicted in FIG. 4 d can be used to announce incomingcalls in a telecommunications terminal. This waveform can be frequencymodulated 14, making different alerting tones, even music, possible. Theemitted sound can be a multichannel stereophonic sound if severalseparately controlled piezoelectric elements are available.

When a piezoelectric element is to be used to generate a vibratingalarm, the used frequency is lower and the audible sound is subdued. Away to achieve a more silent alarm is to make the leading edge of thewaveform somewhat slanted. A typical simple vibration signal with thisleading edge slant 15 is depicted in FIG. 4 e. When needed, morecomplicated vibrational alerts can be generated in the same way as wasdescribed for the different keypress error signals. In FIG. 4 f isdepicted such a multiple vibrating alert, consisting of separate groupsof vibrations. Although not shown, it is possible to use a non-slantedleading edge waveform if audible alerting is needed in addition tosilent vibration alerting.

FIG. 5 shows an electric circuit with a piezoelectric element. Thecircuit of FIG. 5 can be used, for instance, in connection with thecontroller 8 shown in FIG. 1 b.

In FIG. 5 the piezoelectric element 3 is controlled by the controller 8using a switch 21 to control the current flow from the power supply 16.The power supply is only indicated, as it can be considered as known artto build a suitable power supply generating a voltage of 150 . . . 200VDC with a current capability in the milliampere range from a lowvoltage source. The output voltage of such power supply can alsorelatively easily be arranged to be adjustable by a controller.

The power supply 16 as well as the controller 8 are both preferablypowered from the same low voltage power supply 17, which typically isthe battery of a portable terminal.

Each piezoelectric element is connected to at least one switch 21controlled 22 by the controller 8 or contained in the controller. Eachpiezoelectric element can also be controlled by multiple switches andthe controller can also independently control multiple piezoelectricalelements.

The controller 8 controls the operation of a piezoelectric element withthe help of a switch. The switch 21 is typically a high-voltagetransistor. The controller operates the switch to generate suchwaveforms over the piezoelectric element 3 that were depicted in FIG. 4.

In order to vary the leading edge of the waveform and give it a slant avariable serial resistor 19 can be inserted in the circuit. Only manualadjustment is shown in FIG. 5 in order to keep the example circuitsimple.

The voltages acting on the piezoelectric element 3 are shown by way ofexamples in FIGS. 6 a and 6 b. To discharge the piezoelectric element 3a bleeding resistor 20 is connected across the element. This resistormainly affects the lagging edge 32 of the waveform over the element.Because it does not change the audible alerts or perceived vibrationsamplitude as much as he serial resistor 18, it can advantageously be afixed resistor.

The serial resistor 19 adjusts the level of the audible vibrations bychanging the slant 31 of the leading edge, as indicated in FIG. 6 a. Itcan be used to make the slow vibrational alerts inaudible.

In FIG. 6 b is exemplified how the terminal voltage 30 decreases to thelevel indicated by 33 when the resistance of resistor 19 is increased toincrease the slant of the leading edge 31 in order to make the vibrationalert less audible. The capacitance of the piezoelectric elementtogether with any serial resistor forms an RC circuit. The terminalvoltage of this RC circuit decreases because it is dependent on thevoltage divider formed by the serial resistor 19 and the bleederresistor 20. The perceived vibrational alerting amplitude is dependingon the terminal voltage 30, so the vibrational intensity decreases whenthe serial resistance is increased, but this can be compensated byincreasing the level of the power supply voltage 18 to give the earlierterminal voltage over the element and thus give the user the sameperceived vibration intensity.

FIG. 7 shows another electric circuit with a piezoelectric element. Thecircuit of FIG. 7 can be used, for instance, in connection with thecontroller 8 shown in FIG. 1 b.

In FIG. 7 is shown a circuit incorporating voltage control 28 by thecontroller 8. When the controller is operating 22,24 the switches 21,23in various combinations to select various amounts of serial resistance,it simultaneously compensates by controlling 28 the power supply 16 tochange the output voltage 18 in order to keep the terminal voltageacting on the piezoelectric element constant. The vibrational amplitudewill thus stay constant regardless if the user wants sound or no soundwith the vibration.

FIG. 7 depicts how the controller controls 22,24 a single piezoelectricelement 3 with the help of multiple switches 21,23. The multipleresistors 26,27 in FIG. 7 replaces the serial resistor 19 in FIG. 5. Theparallel combinations of switched resistors can form a binary sequenceof serial resistance or otherwise be of any suitable value for theapplication.

Although not shown, the controller 8 can independently controladditional piezoelectric elements. Each independent element will haveits own switch or switches separately controlled by the controllerthrough additional control lines like the set of control lines 22, 24depicted in FIG. 7. The possibility to control multiple elementsseparately in sequence can be used to enhance the vibrational tactilefeeling experienced by the user.

It is to be understood that the above description and the accompanyingdrawings are only intended to illustrate the present invention. Itshould thus be understood that the invention is not restricted to beused only in connection with media terminals even though the inventionhas been explained by way of example in connection with media terminals.It will be obvious to those skilled in the art that the invention can bevaried and modified also in other ways without departing from the scopeand spirit of the invention disclosed in the attached claims.

1. A media terminal comprising: means for establishing telecommunicationconnections; a touch screen keypad; means for generating a tactileresponse to a user of the media terminal when a key in said keypad ispressed, said means for generating a tactile response include at leastone piezoelectric element configured to generate vibration which isforwarded to the user via a key when said key is pressed and said mediaterminal is configured to generate an alerting vibration signal withsaid at least one piezoelectric element in response to an incoming call;wherein said at least one piezoelectric element is configured to contactsaid touch screen keypad in order to cause at least an upper surface ofsaid touch screen keypad to vibrate when said key on the touch screenkeypad is pressed; and a controller configured to: identify a selectedkey in said keypad pressed by the user, check whether the selected keyis available as an option or is not available as an option at the momentthe selected key was pressed, control said at least one piezoelectricelement to generate a first kind of vibration which is forwarded to theuser of the media terminal via the selected key if said check indicatesthat the selected key is not available as an option, and control said atleast one piezoelectric element to generate a second kind of vibrationwhich is forwarded to the user of the media terminal via the selectedkey if said check indicates that the selected key is available as anoption.
 2. A media terminal comprising: a radio transmitter and a radioreceiver for establishing connections; a touch screen keypad; at leastone piezoelectric element for generating a tactile response to a user ofthe media terminal when a key in said keypad is pressed, said at leastone piezoelectric element is configured to generate vibration which isforwarded to the user via a key when said key is pressed and said mediaterminal is configured to generate an alerting vibration signal withsaid at least one piezoelectric element in response to an incoming call;wherein said at least one piezoelectric element is configured to contactsaid touch screen keypad in order to cause at least an upper surface ofsaid touch screen keypad to vibrate when said key on the touch screenkeypad is pressed; and a controller configured to: identify a selectedkey in said keypad pressed by the user, check whether the selected keyis available as an option or is not available as an option at the momentthe selected key was pressed, control said at least one piezoelectricelement to generate a first kind of vibration which is forwarded to theuser of the media terminal via the selected key if said check indicatesthat the selected key is not available as an option, and control said atleast one piezoelectric element to generate a second kind of vibrationwhich is forwarded to the user of the media terminal via the selectedkey if said check indicates that the selected key is available as anoption.
 3. The media terminal according to claim 2, wherein: said keypadincludes a plurality of keys divided into at least two groups of keys,the media terminal includes at least one piezoelectric element for eachgroup of keys, and the media terminal comprises a controller configuredto identify the group of keys to which a pressed key belongs, and tocontrol the piezoelectric element of the identified group of keys togenerate vibration which is forwarded to the user of the media terminalvia the pressed key when said key is pressed.
 4. The media terminalaccording to claim 2, wherein the media terminal includes a controllerconfigured to identify said selected key in said keypad pressed by theuser and to control a piezoelectric element to generate a vibrationwhich is forwarded to the user of the media terminal via the selectedkey to identify the selected key to the user with the help ofvibrations.
 5. The media terminal according to claim 2, wherein saidmedia terminal is configured to generate an alerting sound signal withsaid at least one piezoelectric element in response to an incoming call.6. The media terminal according to claim 2, wherein said media terminalcomprises a controller to alter a shape of a waveform impressed upon thepiezoelectric element.
 7. The media terminal according to claim 2,wherein said media terminal comprises a controller to alter a voltage ofa waveform impressed upon the piezoelectric element.
 8. A methodcomprising: configuring at least one piezoelectric element to generate atactile response to a user of a media terminal when a key in atouchscreen keypad is pressed, wherein the piezoelectric element isconfigured to contact the touch screen keypad in order to cause at leastan upper surface of the touch screen keypad to vibrate when a key on thetouch screen keypad is pressed; configuring the media terminal togenerate an alerting vibration signal with the at least onepiezoelectric element in response to an incoming call; identifying aselected key of the keypad pressed by the user; checking whether theselected key is available as an option or is not available as an optionat the moment the selected key was pressed; controlling thepiezoelectric element to generate a first kind of vibration which istactilely forwarded to the user of the media terminal via the selectedkey if the check indicates that the selected key is not available as anoption; and controlling the piezoelectric element to generate a secondkind of vibration which is tactilely forwarded to the user of the mediaterminal via the pressed key if said check indicates that the pressedkey is available as an option.
 9. The method of claim 8, whereincontrolling the piezoelectric element to generate at least one of thefirst and second kind of vibrations comprises altering a shape of awaveform impressed upon the piezoelectric element.
 10. The method ofclaim 8, wherein controlling the piezoelectric element to generate atleast one of the first and second kind of vibrations comprises alteringa voltage of a waveform impressed upon the piezoelectric element.